1. Field of the Invention
This invention relates to a system for publishing data by broadcast or related technology. More specifically, this invention relates to a system for publishing data on shared channels using spread-spectrum techniques.
2. Description of Related Art
Data publishing is the process of transmitting data to recipients by means of electronic communication channels, such as broadcast or related communication methods. One motive for data publishing is that it may be easier or less expensive to transmit data to recipients by means of broadcast than it would be to write that data onto physical media (such as paper or magnetic disks or tapes) and carry the physical media to them. Another motive is that the marginal cost of publishing the same data to an additional recipient may be comparatively small. Data publishing may be particularly advantageous when the data to be published are voluminous, rapidly changing, or must be delivered within a short time to be useful. A classic example of such data is stock-market trading data, although there are many other cases where data publishing would be advantageous.
One problem which has arisen in the art is the lack of sufficient broadcast infrastructure for data publishing. There are few if any broadcast towers, repeaters, or receivers for use with data publishing, so it has been generally necessary to use infrastructure which is already associated with another form of communication. Hence the use of telephone, television, radio and satellite systems noted above. Accordingly, it would be advantageous to provide a method of data publishing which did not require construction of large amounts of additional infrastructure.
Another problem which has arisen in the art is that it may be difficult to obtain sufficient bandwidth, at reasonable cost and without excessive difficulty, to publish the data. Lack of bandwidth naturally either reduces the amount of data which can be published, or increases the amount of time which is required to publish the data to recipients.
One method of the prior art is to make use of spare bandwidth from an extant communication system. Examples include telephone (using data-over-voice), television (using vertical blanking intervals), and radio (using FM sidebands) systems. While this method achieves a limited degree of success, it has been subject to the drawback that it has not been able to deliver bandwidth to support publishing of large amounts of data. For example, while television systems have a great deal of broadcast bandwidth, the amount of bandwidth for data publishing available by means of the vertical blanking interval is relatively limited. Another problem is that this prior art method does not generally provide national coverage.
Another method of the prior art is to allocate separate frequency bands in which to publish the data. Examples of this method include satellite systems with dedicated channels. While this method is able to deliver a greater amount of bandwidth for data publishing, it has been subject to the drawback that allocation of separate frequency bands for data publishing may generally require proceedings before the FCC or other government agencies.
Another method of the prior art is to use leased lines or other telephone lines to publish the data serially to multiple receiving sites. While this method is able to deliver the data to receiving sites, it has been subject to the drawback that it requires a great deal of money in leased line charges or telephone charges, and therefore may not be economical.
Accordingly, it would be advantageous to provide a method of data publishing which allowed easier access to sufficient bandwidth for data publishing.